1. Field of the Invention
The present invention relates to an anti-skid control system for an automotive vehicle, wherein brake pressure in each wheel brake cylinder is controlled in accordance with pressure control modes including a pulse pressure increase mode.
2. Description of the Related Arts
Various anti-skid control systems have been proposed heretofore to prevent a wheel from being locked during a braking operation of a vehicle. For example, Japanese Patent Laid-open Publication No.8-150918 discloses an anti-skid control system which is adapted to compare a wheel acceleration with a vehicle acceleration at a predetermined time, and adjust a pressure increasing rate of braking pressure, based upon the result of comparison. According to that publication, in view of a prior anti-skid control system as disclosed in Japanese Patent Laid-open Publication No.4-345567, which was aimed to provide an appropriate pressure increasing rate in accordance with the slip rate under such a condition as the coefficient of friction of a road (hereinafter, abbreviated as a road .mu.) or the like is constant, thereby to achieve an ideal braking force control, it was proposed to solve such a problem that the ideal braking force control could not necessarily be achieved by that prior anti-skid control system, when the condition such as the coefficient of friction of the road was varied.
According to the anti-skid control system as disclosed in the aforementioned Japanese Patent Laid-open Publication No.8-150918, however, when a vehicle travels on a rough road, which includes unpaved road, stone pavement, snow road or the like, it will not be easy to perform the anti-skid control operation appropriately, because not only the road .mu. will vary, but also the vehicle wheels will vibrate. This is because the detected wheel acceleration will include the variation due to disturbance caused by change of the road surface, so that comparing the wheel acceleration with the vehicle acceleration at the predetermined time, i.e., at the specific time determined in advance will result in the comparison between the wheel acceleration and the vehicle acceleration including the variations caused by the disturbance of the road surface.